As far as RFC3325 says, that is IMHO not correct. In previous versions of the PBX was was a little bit "messy". The idea of RFC3325 is that the From header can go through all proxies unchanged, and the authentication part is done on other headers.
I know that the support out there for this is weak. Probably the biggest problem is that many ITSP are using SER, which did not support this for a long time. But somehow we have to get started with the standard, that is why the latest and the greatest is strictly according to the RFC.